[FIX] collaborative: snapshot when leaving spreadsheet

Purpose
-------

Let's say a user works a lot on a spreadsheet and performs a lot of heavy
operations generating very large revisions (with lots of commands), such as
copy-pasting a very large zone (there's one UPDATE_CELL command per copy-pasted
cell)

If the user does multiple such very large revision, one after the other,
every thing is fine client side.

The next time the spreadsheet is open though: the server needs to load all
those revisions to send them to the client. The revisions can be so large
it can blow up the server memory limit.
The spreadsheet cannot be open anymore.

Solution
--------

The solution proposed here is to snapshot the spreadsheet when the client
leaves the spreadsheet. Next time the spreadsheet is open, the snapshot will
be loaded, and not the revivisions.

There's a catch: snapshotting a spreadsheet kills the local history (CTRL+Z).
For this reason, we only snapshot if there's no other connected client as it
would kill the other users history.

closes #4334

Task: 3940465
Signed-off-by: Pierre Rousseau (pro) <[email protected]>

src/collaborative/session.ts

@@ -159,7 +159,10 @@ export class Session extends EventBus<CollaborativeEvent> {
   /**
    * Notify the server that the user client left the collaborative session
    */
-  leave() {
+  leave(data: WorkbookData) {
+    if (Object.keys(this.clients).length === 1 && this.processedRevisions.size) {
+      this.snapshot(data);
+    }
     delete this.clients[this.clientId];
     this.transportService.leave(this.clientId);
     this.transportService.sendMessage({

src/model.ts

@@ -288,7 +288,7 @@ export class Model extends EventBus<any> implements CommandDispatcher {
   }
 
   leaveSession() {
-    this.session.leave();
+    this.session.leave(this.exportData());
   }
 
   private setupUiPlugin(Plugin: UIPluginConstructor) {

tests/collaborative/collaborative_session.test.ts

@@ -2,7 +2,7 @@ import { Model } from "../../src";
 import { Session } from "../../src/collaborative/session";
 import { DEBOUNCE_TIME, MESSAGE_VERSION } from "../../src/constants";
 import { buildRevisionLog } from "../../src/history/factory";
-import { Client, CommandResult } from "../../src/types";
+import { Client, CommandResult, WorkbookData } from "../../src/types";
 import { MockTransportService } from "../__mocks__/transport_service";
 import { selectCell } from "../test_helpers/commands_helpers";
 
@@ -50,7 +50,8 @@ describe("Collaborative session", () => {
 
   test("local client leaves", () => {
     const spy = jest.spyOn(transport, "sendMessage");
-    session.leave();
+    session.leave({} as WorkbookData);
+    expect(spy).toHaveBeenCalledTimes(1);
     expect(spy).toHaveBeenCalledWith({
       type: "CLIENT_LEFT",
       version: MESSAGE_VERSION,
@@ -59,6 +60,57 @@ describe("Collaborative session", () => {
     expect(session.getConnectedClients()).toEqual(new Set());
   });
 
+  test("local client leaves with no other clients and changes", () => {
+    transport.sendMessage({
+      type: "REMOTE_REVISION",
+      version: MESSAGE_VERSION,
+      nextRevisionId: "42",
+      clientId: "client_42",
+      commands: [],
+      serverRevisionId: transport["serverRevisionId"],
+    });
+    const spy = jest.spyOn(transport, "sendMessage");
+    const data = { sheets: [{}] } as WorkbookData;
+    session.leave(data);
+    expect(spy).toHaveBeenCalledWith({
+      type: "SNAPSHOT",
+      version: MESSAGE_VERSION,
+      nextRevisionId: expect.any(String),
+      serverRevisionId: "42",
+      data: { ...data, revisionId: expect.any(String) },
+    });
+  });
+
+  test("local client leaves with other connected clients and changes", () => {
+    transport.sendMessage({
+      type: "CLIENT_JOINED",
+      version: MESSAGE_VERSION,
+      client: {
+        id: "bob",
+        name: "Bob",
+        position: { sheetId: "sheet1", col: 0, row: 0 },
+      },
+    });
+    expect(session.getConnectedClients().size).toBe(2);
+    transport.sendMessage({
+      type: "REMOTE_REVISION",
+      version: MESSAGE_VERSION,
+      nextRevisionId: "42",
+      clientId: "client_42",
+      commands: [],
+      serverRevisionId: transport["serverRevisionId"],
+    });
+    const spy = jest.spyOn(transport, "sendMessage");
+    const data = { sheets: [{}] } as WorkbookData;
+    session.leave(data);
+    expect(spy).toHaveBeenCalledTimes(1);
+    expect(spy).toHaveBeenCalledWith({
+      type: "CLIENT_LEFT",
+      version: MESSAGE_VERSION,
+      clientId: client.id,
+    });
+  });
+
   test("remote client move", () => {
     transport.sendMessage({
       type: "CLIENT_MOVED",
@@ -147,7 +199,7 @@ describe("Collaborative session", () => {
 
   test("Leave the session do not crash", () => {
     session.move({ sheetId: "sheetId", col: 1, row: 2 });
-    session.leave();
+    session.leave({} as WorkbookData);
     jest.advanceTimersByTime(DEBOUNCE_TIME + 100);
   });